Mechanism of ONB based on nonequilibrium thermodynamics of natural circulation in narrow channels

Based on the experiment of onset of nucleate boiling(ONB)in natural circulation and the nonequilibrium thermodynamics dissipative theory,the mechanism of ONB in narrow rectangle channels of natural circulation is proposed.It points out that the onset of nucleate boiling is influenced by the degree of superheat and the special conditions of narrow channels.Under the conditions of both density difference in natural circulation and narrow rectangle channels,the prediction model of ONB in natural circulation of narrow channels based on fluctuating is established.The experimental results show that the present model can be used to predict the heat flux of ONB in narrow rectangle channels.Features of ONB in natural circulation narrow rectangle channels are as follows:heating power is the incentive of the happen of ONB;the higher the heating power is,the higher the degree of superheat is,and the earlier the ONB will appear.With the pressurizing,the appearance of ONB will be delayed.The higher the degree of supercooling is,the later the ONB appears.The ONB will happen easier when there are noncondensable gases and roughness in the channels.

Simulation of mesoscale interfacial properties using the lattice Boltzmann method

We derive the mesoscopic interparticle potentials from macroscopic thermodynamics for van der Waals,Redlich-Kwong,and Redlich-Kwong-Soave equations of state and find that all these potentials are very similar to the Lennard-Jones potential.To investigate the interfacial property at the mesoscale level,we incorporate free energy functions into the single-component multiphase lattice Boltzmann model and obtain the saturated density coexistence curves and interface mass density profiles across the interface using this method with different equations of state.The simulation results accurately reproduce the properties of equilib-rium thermodynamics.Numerical results for single-component phase transitions indicate that a bubble-growth process is obtained and the equilibrium phase diagram is achieved at a given temperature.Bulk free energy,the interfacial energy coefficient,and other properties of nonequilibrium thermodynamic parameters,which are used to examine interfacial properties,are obtained in these simulations,and all these parameters are found to obey irreversible thermodynamics.